This invention relates to a DBS (direct broadcast satellite) receiving system, and particularly to an improved method and apparatus for selecting a particular one of a multitude of available satellite signals or groups of signals having a common characteristic or state.
In communication systems, including satellite systems, to expand the number of channels that can be transmitted without interference within a given spectrum it is common practice to broadcast a set of channels or frequency bands using one state of polarization, and another set of channels or frequency bands using an alternate polarization. By way of example, a known DBS system employs satellites transmitting orthogonal LHCP (left hand circular polarization) and RHCP (right hand circular polarization) signals. The number of available channels may also be increased by adding additional transmitters, such as additional satellite transponders. These may be co-located but utilize different frequencies (e.g. C-band and Ku-band), or may be at different locations requiring either separate or multi-focus receiving antennas and electronics.
In a known system the DBS subscriber has an IRD (integrated receiver-decoder) which is used to tune a desired channel from the available channels.
However, because a set of channels is broadcast using one polarization state and another set using an alternate polarization state, the subscriber must have the capability of selecting (automatically through the IRD) a channel from one or the other of the alternately polarized sets of signals.
In known systems, upon user selection of a particular channel the IRD determines whether that channel is being downlinked as a LHCP signal or a RHCP signal. In known manners, it then develops one of two possible constant output voltage states (e.g. 13 volts or 17 volts) associated with the desired polarization state. The constant output voltage is applied to an LNB (low noise block converter) located at the site of the antenna, which decodes the applied output voltage and selects the commanded LHCP or RHCP signals for reception and processing.
However, with additional satellites (e.g. at different locations) or groups of signals (e.g. at different frequencies) becoming available to the DBS subscriber, the two-state voltage command currently used to select one of a set of two possible signal characteristics or states (e.g. polarizations) is no longer adequate. There exists a need to provide, with a minimum of difficulty or expense, remote selection capabilities for controlling multi-state remote equipment (e.g. antenna selection and/or LNB states) which may, in certain embodiments, be compatible with existing IRDs.